Cocarded blend of microcellular and conventional fibers

ABSTRACT

A cocarded blend of 1-80 percent closed-cell microcellular staple fibers and 99 percent to 20 percent dense, substantially noncellular staple fibers is cardable and inexpensive and has desirable bulk, resiliency, load bearing capacity and recovery upon removal of a load.

United States Patent inventor Willard Hallam Bonner, Jr.

Wilmington, Del.

Appl. No. 870,723

Filed Sept. 16, 1969 Patented Dec. 28, 1971 Assignee E. I. duPont deNemours 8: Company Wilmington, Del.

Original application June 23, 1966, Ser. No. 559,979, now Patent No.3,521,328. Divided and this application Sept. 16, 1969, Ser. No. 870,723

COCARDED BLEND OF MICROCELLULAR AND CONVENTIONAL FIBERS 7 Claims, 2Drawing Figs.

U.S.Cl 161/169, 161/178, 5/361 Int. Cl A47c 27/22 PrimaryExaminer-Robert F. Burnett Assistant Examiner-Linda C. KoeckertAttorney-William R. Mose-r ABSTRACT: A cocarded blend of 1-80 percentclosed-cell microcellular staple fibers and 99 percent to 20 percentdense, substantially noncellular staple fibers is cardable andinexpensive and has desirable bulk, resiliency, load bearing capacityand recovery upon removal of a load.

MICROCELLULAR STAPLE FIBERS DENSE, NON" CELLULAR STAPLE FIBERSFAIENIEDUEC28I97I 3 30. 23

FIG. I

FABRIC COVERING STUFFING MATERIAL MICROCELLULAR STAPLE FIBERS DENSE,NON-CELLULAR STAPLE FIBERS FIG. 2

INVENT OR WILLARD HALLAM BONNER, JR.

BY MMM ATTORNEY COCARDED BLEND F MICROCELLULAR AND CONVENTIONAL FIBERSThis application is a division of our copending application Ser. No.559,979, filed June 23, 1966, now US. Pat. No. 3,521,328.

This invention relates to a cocarded fibrous blend suitable for use as afilling material in upholstery cushions, mattresses, sleeping bags,insulated garments, etc. More particularly, the invention relates tococarded mixtures of closed-cell microcellular staple fibers and densestaple fibers, either natural or synthetic.

Batts of randomly oriented natural staple fibers have long been used asstuffing materials for cushions, mattresses and the like, but for manyuses they have a number of inherent disadvantages. More recentlysynthetic fiber staple batts have found commercialacceptance-particularly those formed of the more resilient polyesterfibers such as polyethylene terephthalate fibers. For many purposes,however, these newer materials have been relatively expensive incomparison with their natural fiber counterparts. Accordingly, theeconomics have created a tendency to use only a minimum weight of suchfibers in stuffing a given volume although at a sacrifice to otherproperties such as load support, durability, reflufiability, andappearance.

Still more recently, the problems heretofore associated with even thesynthetic fiber stuffing materials, particularly that of maximum loadsupport at low or economic weights of fiber, would seemingly be obviatedby the pneumatic closed-cell ultramicrocellular synthetic fibers asdescribed in Blades et al. U.S. Pat. No. 3,227,664. Nonetheless, forcertain cushioning applications the unique nature of these low-densitycellular filaments has introduced further considerations, to bediscussed in greater detail later, both with respect to the utilizationof conventional textile equipment and to the attainment of otherdesirable cushioning properties.

in accordance with the invention the deficiencies of such prior artmaterials is overcome by the provision of a composite resilient stuffingmaterial comprised of a cocarded mixture of 1 to 80 percent by weight ofclosed-cell microcellular staple fibers of a synthetic polymer, whichfibers are characterized by having substantially all of the polymerpresent asfilmy elements of a thickness less than 2 microns, togetherwith 99 to 20 percent by weight of dense, substantially noncellularstaple fibers, the cocarded mixture being in the form of an intimate,interentangled blend of said microcellular and dense fibers.

Unexpectedly "has been found that the addition of as little as 20percent by weight of dense fibers, which act as carrier fibers, to themicrocellularfibers permits the formation of highly useful fibrous battsnot only possessing the desirable attributes of each component but, inaddition, having properties not characteristic of either and which wouldbe essential to certain cushioning applications. Significantly thepresence of even such a small amount of dense fibers permits textileoperations such as carding processes which are not feasible with themicrocellular fibers alone. Additionally, a coherent product can beobtained which, owing to the large difference in densities of the fibercomponents, visually appears to be comprised of microcellular fibersalone. In this regard, since the density of the dense staple fibers mayexceed that of the microcellular fibers by a factor of nearly 100 ormore, the presence of as little as 1 percent of the microcellular fibersin such a blend will greatly contribute to bulk,resiliency, loadbearingcapacity and recovery upon removal of a load. Particularly in the caseofcushioning materials such as mattresses and pillows designed for bodycomfort, an optimum range of the fibers is 25 to 65 percent by weight ofmicrocellular fibers and 75 to 35 percent by weight of dense fibers.

The formation of the novel stuffing material of the invention involvesthe use of any standard carding machine and, in most instances, themicrocellular fibers need not previously be converted to staple lengthbecause continuous lengths will'be reduced to staple lengths, say of 1inch or so, by the action of the card.

The invention will be further understood from FIG. 1 which shows inschematic and enlarged form a cushioning article in which the composite,resilient stuffing material of the invention, i.e., which is composed ofa cocarded mixture of microcellular and dense fibers, is sandwichedbetween layers of a covering fabric. It will be understood that thefabric covering and quilted configuration are optional features of theinvention.

FIG. 2 shows an enlarged view of the composite, resilient stuffingmaterial, depicting in detail the cocarded mixture of the closed-cellmicrocellular staple fibers and the dense, noncellular staple fibers.

The invention is importantly dependent upon the character of themicrocellular fibers; that is, they must be of a particular closed-cellvariety so as to be capable of retaining gases therein. Such fibers wheninflated are thus pneumatic, i.e. individual cells acting as miniatureballoons, and a maximum contribution is made both with respect toload-bearing abilities and to thermal insulation properties. However,the invention also contemplates composite stuffing materials, in whichthe microcellular filaments are initially collapsed, i.e. to less thantheir normal or fully expanded thickness. Such products find uniqueutility in manufacturing operations where this relatively compact formfacilitates handling, or where the closed cell nature of themicrocellular filaments permits subsequent in-place" postinflation ofthe products to their full pneumatic potential.

Microcellular filaments employed according to this invention aresubstantially homogeneously foamed throughout to provide closedpolyhedral-shaped cells of less than about 1,000 microns each in maximumtransverse dimension, each cell completely enclosed by thin filmlikepolymeric cells less than about 2 microns thick. By substantiallyhomogeneously foamed throughout is meant not only that there is a narrowdistribution of cell sizes but also that the filament is devoid ofseparately identifiable skins, webs, or casings of dense polymersurrounding the foamed portion; i.e., the outer surface is composed ofthin cell walls. The density of gas-inflated microcellular filaments isin the range of 0.005 to 0.05 g./cc. Dense polymeric skins areundesirable because they can crack upon repeated compressive flexing,because they restrict the pneumatic behavior of the enclosed foam, andbecause their weight per unit volume of enclosed gas is too great toobtain low densities.

Microcellular filaments must have predominantly closed foam cells.Otherwise gases cannot be confined within the cells and a high degree ofpneumaticity of the filaments cannot result. The determination ofclosed-cell contact is ordinarily made by visual or microscopicobservation. Alternatively, a gas displacement technique such as thatdescribed by Remington and Pariser in Rubber World, May i958, p. 26l,can be used if modified to operateat the lowest possible pressuredifferentials. A predominantly closed-cell content is qualitativelyindicated if a gas-inflated microcellular filament feels pneumatic whensqueezed between the fingers and recovers its original size and shapeimmediately thereafter.

Microcellular filaments must also be yieldable and resilient such thatsubstantial cross-sectional deformation results from externally appliedcompressive loads. Generally, this requirement is satisfied if agas-inflated filament is reduced in thickness by at least 10 percentunder a load of [0 psi. (0.70 kg./cm. based on an area computed from thelength and original diameter, the load being maintained for I second,and if there is an immediate thickness regain to at least 50 percent,and preferably to substantially percent, of the original thickness onrelease of the load.

A particularly desirable microcellular filament for use in the productsof this invention is ultramicrocellular as disclosed by Blades et al. inUS. Pat. No. 3,227,664. Ultramicrocellular filaments are additionallycharacterized in that the polymer in their thin cell walls exhibitsuniplanar orientation and uniform texture as described in said patent.These latter two properties provide the surprisingly great strength ofthe filaments and render their cell walls particularly resistant to gaspermeation.

A wide variety of both addition and condensation polymers can formmicrocellular filaments with the essential characteristics. Typical ofsuch polymers are: polyhydrocarbons such as polyethylene, polypropylene,or polystyrene; polyethers such as polyformaldehyde; vinyl polymers suchas polyvinyl chloride or polyvinylidene fluoride; polyamides such aspolycaprolactam, polyhexamethylene adipamide, or polymetaphenyleneisophthalamide; polyurethanes such as the polymer from ethylenebischloroformate and ethylene diamine; polyesters such aspolyhydroxypivalic acid or polyethylene terephthalate; copolymers suchas polyethylene t'erephthalate-isophthalate; polynitriles such aspolyacrylonitrile or polyvinylidene cyanide; polyacrylates such aspolymethylmethacrylate; and equivalents.

Planar molecular orientation of the polymer in the cell wallscontributes significantly to the strength of the filaments. A preferredclass of polymers for forming suitable microcellular filaments is,therefore, one including those which respond to orienting operations bybecoming tougher and stronger. This class includes linear polyethylene,stereo-regular polypropylene, polycaprolactam, polyethyleneterephthalate, polyvinyl chloride, and the like. Further preferred isthe class of polymers known to be highly resistant to gas permeation,such as polyethylene terephthalate and polyvinyl chloride.

The microcellular filaments employed preferably contain sufficientimpermanent inflatant to provide a total internal pressure within thecells of at least atmospheric pressure. An impermeant inflatant is a gaswhich permeates the cell walls so slowly as compared to air that it issubstantially permanently retained within the cells. The presence ofimpermeant inflatant within the cells creates an osmotic gradient forthe inward permeation of air (or other ambient gaseous atmosphere).Thus, at equilibrium with air, the cells of microcellular filamentscontain not only air at about one atmosphere but also impermeantinflatant at a given partial pressure. The combined pressure, then, isat least atmospheric and guarantees that the filaments are fully gasinflated and turgid. Loss of air by permeation during compression isordinarily insufficient to prevent full reinflation immediately uponrelease of the load. If, however, full reinflation does not resultimmediately, the osmotic gradient provided by the impermeant inflatantcauses spontaneous reinfiation by equilibration with ambient air.

The rate of permeation for an inflatant gas through a given polymerincreases as its diffusivity and solubility increase. Accordingly,impermeant inflatants should have as large a molecular size as isconsistent with providing the required vapor pressure and should havevery little or no solvent power for the polymer. A preferred class ofimpermeant inflatants is exemplified by compounds whose molecules havechemical bonds different from those found in the confining polymer, alow dipole moment, and a very small atomic polarizability.

Suitable impermeant inflatants are selected from the group consisting ofsulfur hexafluoride and saturated aliphatic and cycloaliphatic compoundshaving at least one fluorine-to-carbon covalent bond and wherein thenumber of fluorine atoms preferably exceeds the number of carbon atoms.Preferably the saturated aliphatic and cycloaliphatic compounds are,respectively, perhaloalkanes and perhalocycloalkanes in which at least50 percent of the halogen atoms are fluorine. Although these inflatantsmay contain ether-oxygen linkages, they are preferably free fromnitrogen atoms, carbon-to-carbon double bonds, and reactive functionalgroups. Specific examples of impermeant inflatants include sulfurhexafluoride, perfluorocyclobutane, sym-dichlorotetrafluoroethane,perfluorol ,3dimethylcyclobutane, perfluorodimethylcyclobutane mixtures,l l ,2-trichlorol ,2,2-trifluoroethane, CEQCE2QEZQCFHCF3,chlorotrifluoromethane, and dichlorodifluoromethane. Mixtures of two ormore impermeant inflatants can often be used to advantage.

The dense, substantially noncellular, staple fibers suitable for use inthis invention may be either natural fibers such as cotton, kapok,animal hair etc. or synthetic fibers such as polyamides, polyesters,polyhydrocarbons, rayons, etc. They are quite dense in comparison withthe microcellular fibers,

ordinarily having a density of at least 0.8 g./cc. and usually at least1.0 g./cc. Although often containing a few random closed or open cells,they are essentially noncellular. Staple fibers of polyethyleneterephthalate are preferred due to their high resilience, chemicalinertness, resistance to moths, etc. These fibers are conventionallysupplied as a batt of fibers in more or less random array, as preparedfor example on the Garnett machine or a random webber. The utilizationof staple fibers is further advantageous because of the fiber mobility.resilience and high recovery afforded.

In a particularly preferred embodiment, both the microcellular filamentsand the dense staple fibers are composed of polyethylene terephthalate.Such a blend is advantageous not only from the standpoint that these twotypes of fibers have individually superior cushioning characteristicsand other properties, but also for the reason that generally lower bulkdensities can be employed while obtaining a given degree of loadsupport.

Although pneumatic microcellular fibers could be employed as the solestuffing material in certain cushioning applications to provide verylow-density resilient and pneumatic fillings, such fillings neverthelesshave a relatively high compression modulus and consequently may be toofirm for optimum comfort. ln marked contrast, the percent dense fiberstaple fillings tend to be unduly soft, particularly at the low stuffingdensities which are often required by reason of the economics involved.The present invention effectively overcomes these previous deficienciesand provides intermediate degrees of firmness and softness byappropriate selection of the ratio of components. In addition to theprovision of aesthetically very desirable stuffing materials, theinvention further provides the manufacturer with the advantage of beingable to supply a diverse range of stuffing materials tailored to meetindividual compressibility requirements from a stock of only twocomponents.

The microcellular fibers, when fully inflated may have diameters varyingover a very wide range, e.g. 0.008 inch to 0.4 inches. For mostcushioning applications, however, they will preferably have diameters ofless than about 0.05 inch.

The intimately blended batts of this invention are formed in a cocardingoperation. The microcellular fibers by themselves cannot be carded onconventional textile machinery owing to their large diameter whichprevents a sufficient degree of fiber entanglement necessary to producea coherent web or mass. However, it has been discovered that addition of20 percent by weight or more of dense staple fibers makes the cardingoperation feasible, as well as contributing desirable properties to theblended stufiing material. It is a further surprising feature that themicrocellular fibers may be furnished either as staple or continuousfilament. Thus, when a standard wireclothed sample card or ametal-clothed garnett card is employed, the continuous filamentmicrocellular fiber is adequately converted into the desired lengthstaple during the carding operation by the tearing action between themain cylinder and the licker-in, worker and stripper rolls. Bothinflated and collapsed postinflatable microcellular fibers operatesatisfactorily in the cocarding operation. It is noteworthy in thisrespect that even the collapsed microcellular fibers alone cannot beeffectively carded since again, the filament diameters are unduly large.

A furnish for the carding operation is conveniently formed by supplyinga crude sandwich of desired proportions by weight of dense fiber battssurrounding a layer of microcellular fibers, as might be directlypiddled onto a conveyor belt, for example. The carding operationresponds favorably to application of fiber finishes to the microcellularfibers to assist in decreasing any static generated. The blended cardedweb can be wound up directly on a roll, sewn to a cheesecloth backing,or built up in layers to any desired thickness as by a camelback lapper.These blended webs may either be used directly as stuffing materials orstored indefinitely for later use as desired.

lf the stuffing materials of this invention have been prepared fromcollapsed cellular fibers, they may be inflated either before or afterthe stuffing operation.

The stuffing materials may conveniently be handled with a conventionalpillowor cushion-stuffing machine, they may be stuffed by hand, or thebatt may be quilted between covers as in preparation of comforters,sleeping bags, insulated clothing, and the like. The blended batts maybe impregnated if desired with elastic adhesives to further enhance battcoherence and minimize fiber packing. Flameproofing agents, and thelike, can also beadded, either by spray or dip.

The following examples illustrate a number of the features of thisinvention. The low-density synthetic organic cellular fiber component,in each example, is comprised of polyhedralshaped cells whose filmy cellwalls are less than 2 microns thick. The cellular components in example1 through example 1X are the preferred ultramicrocellular species wherein addition the filmy cell walls exhibit uniform texture and uniplanarorientation.

EXAMPLE I Polyethylene terephthalate ultramicrocellular foam fiberscontaining a quantity of perfluorocyclobutane were spun from a solutionof 400 parts polyethylene terephthalate, 325 parts methylene chloride,42 parts dichlorodifluoromethane and 42 parts of perfluorocyclobutane(all parts by weight) extruded at a temperature of 210 C. and a pressureof 1,000 p.s.i. through a 24-hole spinneret, each hole being 4 mils indiameter. The filaments had a tenacity of 0.44 g.p.d., and a denier of48 (5.3 tex), and a relative viscosity of 25. When fully inflated andequilibrated with air these pneumatic filaments had a density of 0.022g./cc. and a diameter of 23 mils.

A quantity of these continuous filament inflated ultramicrocellularfibers was distributed evenly over an equal weight gametted batt of 4d.p.f. (0.44 tex) polyethylene terephthalate 2-inch staple fibers, fiberdensity of 1.38 g./cc., and run through a standard metal-clothed garnettcard manufactured by Proctor and Schwartz. The garnett card had a30-inch diameter main cylinder, a 20-inch diameter doffer cylinder, a-inch diameter licker-in roll, 4 worker rolls each 7 inches in diameter,4 stripper rolls each 3 3/16 inches in diameter, and top and bottom feedrolls each 3 inches in diameter. All rolls were inches in diameter andwere covered with metallic clothing.

The fibers processed well to form an intimately blended carded batt ofultramicrocellular/dense fibers having an overall density of only 1.2lbs/cu. ft. The continuous filament cellular fibers were reduced to anaverage staple length of 1 inch by the carding operation.

The above example was repeated substituting continuous cellularfilaments spun from a 3-mil multihole spinneret. These filaments had adensity of 0.03 grams per cc. and an inflated diameter of 12 mils. Theyprocessed equally well to yield a blended batt of density 0.7 lbs./cu.ft.

These batts were quite resilient and exhibited excellent recoveryproperties from deformation due to their impermeant perfluorocyclobutanecontent and the mobility of the carded fiber structure. They were highlysuitable for use as stuffing materials in upholstery cushions,comforters, sleeping bags, insulating garments and the like.

EXAMPLE [1 fiberfill in a 50/50 weight ratio and carded on a standardgarnett card. Well-blended uniform battings were produced in which thecellular filaments had been reduced to lengths ranging from [/2 to 16inches.

The collapsed cellular filaments in the batting were readilypostinflated. One suitable technique was to immerse the batt in aboiling 50/50 volume mixture of methylenechloride/l,1,Z-trifluoro-l,2,2-trichloroethane for 15 minutes. Anequally satisfactory technique was to immerse the butt in a boiling /20volume mixture of 1.2-dichlorotetrafluoroethane/methylene chloride for30 minutes followed by drying in an air oven at C. The volume of thebatting increases markedly as the cellular filaments reexpand to theiroriginal low density of 0.022 grams per cc. The bulk density of thispostexpanded batting was only 0.31 lbs/cu. ft. The dense polyesterfiberfill in the batt was difficult to see, being obscured by the muchbulkier expanded cellular filament whose inflated diameter is 18 mils.

EXAMPLE 111 A collapsed ultramicrocellular polyethylene terephthalateyarn of density 0.l 1 grams per cc. was spun directly from a 4- milmultihole spinneret. Collapsed filaments result when the impermeantinflatant is omitted from the spinning solution. This yarn was passeddirectly from the spinneret through a hand-held air-operated jet andthus deposited in a batt of randomly oriented continuous filaments. Thisbatt was sandwiched in a 50/50 weight ratio with commercial samples ofpolyethylene terephthalate fiberfill batting. The sandwich was fedthrough a standard garnett card and rolled up manually. Thorough anduniform distribution of foam and polyester fiberfill was obtained. Foamfiber length in the carded batting varied from l/2 to 7 inches with anaverage length of 2 to 3 inches. The foam fibers appeared to be themajor component in the batting. The collapsed foam fibers in the blendedbatt were subsequently postexpanded by the techniques described in thepreceding example.

EXAMPLE 1V Mixtures of the following parts by weight of foam fiber/densefiber of polyethylene terephthalate were prepared:'

6/94; 30/70; 50/50; 70/30; and 80/20. These mixtures were supplied asthe furnish to the standard garnett card. The carded blends were takenfrom the card on a moving belt and lapped to a uniform package. Allbattings showed uniform foam/dense fiber distribution. The first threeblends processed well, while the blend containing 70 percent foam fiberprocessed marginally because the lightweight batting did not releaseuniformly from the compacting roll. The blend containing 80 percent offoam fiber could be processed through the card, but it was necessary toroll it up manually. The dense fiber staple was necessary to the cardingof the foam fibers. One hundred percent foam fiber could not beprocessed in the garnett card.

EXAMPLE V Staple lengths (2 inches) of polyethylene terephthalate foamfilaments were mixed with polyethylene terephthalate dense fiber staplein a 50/50 by weight mixture. This mixture was processed on a standardgarnett card to form an intimately blended batt. The 2-inch staplelength foam fibers were further broken up during the carding operationto an average length of 0.8 inch. This mixture of foam and dense staplefibers processed well in the carding operation.

EXAMPLE V1 Collapsed polyethylene terephthalate foam filaments were spundirectly from a 3-mil multihole spinneret. A portion was cut into 2-inchstaple lengths. These collapsed foam fibers have a diameter ofapproximately 7 mils, a tenacity of approximately 1 gram per denier, andwere approximately 10 denier per filament. The continuous filament(portion A) and staple (portion B) were each mixed at 50/50 weightratios with polyethylene terephthalate fiberfill and processed on aconventional sample card having fillet clothing on the main cylinder andmetallic clothing on the worker and stripper rolls, manufactured byDavis and Furber (Phila.). Portion B processed well, as did portion Awhen the precaution of a moderate feed rate was observed to prevent cardjamming. The average foam fiber length in portion A was reduced to 2.3inches and in portion B to 1.9 inches by the carding operation.

The blended batts of collapsed foam filaments were postinflated by a-minute treatment in a boiling bath of a 50/50 weight mixture ofperfluorocyclobutane/fiuorodich loromethane. The densities of thepostinflated batts of portions A and B were 0.33 l6./cu. ft. and 0.43lb./cu. ft., respectively. The tactile aesthetics as well as thecompression characteristics of these blended fibrous composites arejudged superior to those of corresponding 100 percent foam filamentbatts.

EXAMPLE Vll A fibrous cushioning structure was prepared by cocarding a70/30 (weight) mixture of polyethylene terephthalate ultramicrocellularfoam fiber/cotton staple fiber. The ultramicrocellular fibers werefurnished as a random batt of continuous filaments of 17-20 d.p.f.(approximately 2 tex) and density of 0.030 g./cc., the individualinflated cells containing a quantity of spun-in perfluorocyclobutane anddichlorodifluoromethane (impermeant inflatants). The cotton componentwas prepared as a garnetted batt from SO-grain sliver El Paso cotton, of1%- inch staple length, and 12-1 .6 d.p.f. (approximately 0.15 tex). Tofacilitate preparation of the gamctted cotton batt, the previouslyfinish-free sliver was sprayed with a commercial antistat finish. Thedense and foam fiber batts were sandwiched and fed to a garnett card, asin previous examples, whereupon an intimate blend was produced and thecontinuous filament polyethylene terephthalate foam yarns were broken upinto staple lengths. Application of talc, dusted onto the cocarded batt,facilitated release of the batt from the card and subsequent transferand handling operations.

A 3-inch thick cushion was stuffed to a density of 1.4 lb./cu. ft. withthis cocarded fiber blend. A similar reference cushion was stuffed to adensity of 3.6 lb./cu. ft. with a 100 percent cotton garnetted batt(same cotton used for preparing the blend). In spite of the fact thatthe density of the blended batt cushioning was only 39 percent that ofthe reference cushion, the load support of the blended batt cushion wasgreatly superior (only 34 percent compression vs. 52.5 percentcompression for the reference cushion under 1 p.s.i.g. loads).

EXAMPLE VllI Ultramicrocellular filaments of linear polypropylene wereprepared by charging a one liter pressure vessel with 300 grams linearpolypropylene, 325 ml. methylene chloride, 50 grams symmetricaldichloro-tetrafluoroethane and 2.5 grams of Santocel 54 (a finelydivided silica aerogel employed here as a bubble nucleating assistant).The pressure vessel was closed, heated to 180 C. and rotated slowlyend-over-end for about 16 hours to achieve good mixing and solution ofthe contents. The pressure vessel was then positioned vertically, thetemperature of the solution decreased to 150 C. and a pressure of 950p.s.i.g. of nitrogen applied just prior to extruding the solutionthrough a l2-hole spinneret, each hole 4 mils diameter by 8 mils longlocated at the lower extremity of the pressure vessel. Flash evaporationof the methylene chloride as the solution issued from the spinneretgenerated ultramicrocellular strands of linear polypropylene having adensity of 0.012 grams per cc., a tenacity of 0.8 g.p.d. and being 34d.p.f. (3.8 tex).

These linear polypropylene ultramicrocellular filaments were collectedas a random batt which was sandwiched between gametted polyethyleneterephthalate fiberfill staple batts in a 70/30 weight ratio of foamfibers/dense fibers. This composite batt was fed through the garnettcard as in previous examples, whereupon an intimate uniform blend wasproduced, and the ultramicrocellular continuous filaments were reducedto approximately 2-inch average staple length.

A 3-inch thick cushion was stuffed with this blend to a density of only0.7 lb./cu. ft. Even at this extremely low density,

this cushion showed better support under 1 p.s.i.g. load than areference cushion stuffed to 3.4 lb./cu. ft. with 100 percentpolyethylene terephthalate fiberfill, or another reference cushion of5.0 lb./cu. ft. foam rubber (commercial sample), or another referencecushion of 1.6 lb./cu. ft. polyurethane foam (commercial sample).

EXAMPLE [X A cocarded batt was prepared as in previous examples from a50/50 weight mixture of polyethylene terephthalate fiberfill staple andpolyethylene terephthalate ultramicrocelluar fibers. The lattercontained a quantity of dichlorodifluoromethane and perfluorocyclobutaneas impermeant inflatants, had a density of 0.04 g./cc., a tenacity of0.8 g.p.d. at a denier per filament of 15-20 (about 2 tex).

A 70-gram portion of this batt was used to fill a perforated metal cage8% inches X 8% inches X 5 inches which was then dipped in a 4 percentsolution of a commercial urethane polymer adhesive in1,1,2-trichloroethane. When the excess solution had drained through thecage, the batt was dried in a circulating air oven at 250 F. (about 121C.) for one-half hour. The batt picked up 20 g. of the elastic adhesivewhich resulted in increased coherence and durability. This bonded batthad a density of only 0.98 lb./cu. ft. and was compressed 17 percent at0.2 p.s.i.g. (14 g./sq. cm.), 48 percent at 0.6 p.s.i.g (42 g./sq. cm.),and 61 percent at 1.0 p.s.i.g. (70 g./sq. cm.).

EXAMPLE X Partially collapsed polypropylene microcellular filaments wereprepared by blending in a heated extruder equal parts by weight ofisotactic polypropylene (Hercules ProF ax" 6223) andfluorodichloromethane. The resulting solution was extruded at 170 C. and1,250 p.s.i.g. (about atm.) through a cylindrical orifice 4.5 mildiameter X 8 mils long (114x203 microns) to generate a microcellularfilament as the superheated solvent flashed off. These microcellularfilaments were comprised of polyhedral cells defined by textured wallsless than 2 microns thick. After equilibrium with ambient air wasestablished, the filaments were in a partially deflated condition with adensity of 0.0249 g./cc., a diameter of 14 mils (0.36 mm. a tenacity of0.4 g.p.d.

These partially collapsed microcellular filaments were fed with an equalweight of commercial polyethylene terephthalate fiberfill batting to astandard garnett card. During the blending operation the microcellularcontinuous filament component was reduced to staple of l to 4 cm. inlength. The microcellular and dense fibers were uniformly distributed inthe blended batt thus prepared. The blended batt was subsequentlyexposed under pressure for 30 minutes to an atmosphere ofperfluorocyclobutane vapor in equilibrium with the liquid phase at 55 C.followed by a l5-minute heating in an air oven at C., which treatmentfully inflated the microcellular component filaments to a density of0.0132 g./cc. and a diameter of 23 mils (0.58 mm.). These particularpolypropylene microcellular filaments, although apparently still fullyinflated, were observed to have lost all their perfluorocyclobutaneinflatant within a few days after the postinflation treatment. Thisrelatively rapid loss of inflatant is attributed at least in part to thefact that the cell walls do not exhibit uniform texture.

The blended foam/dense fiber batting was stuffed into a cotton tickingto provide a 6%-inch (approximately 17 cm.) diameter test cushion ofapproximately 4 inches (10 cm.) height. The initial filling density of0.92 lb./cu. ft. increased to 1.26 lb./cu. ft. upon overnight exercisingof the cushion to a 1% /&p.s.i. (approximately g./sq. cm.) load 8,000cycles. This blended batting thus affords useful cushioning abilityalthough its durability to cyclic loading is not so good ad that ofcomparable blended batts prepared from ultramicrocellular foamed fibers.

What is claimed is:

l. A composite resilient stuffing material comprised of a cocardedmixture of l to 80 percent by weight of closed-cell microcellular staplefibers of a synthetic organic polymer and characterized by havingsubstantially all of the polymer present as filmy elements of athickness less than 2 microns, together with 99 to 20 percent by weightof dense, substantially noncellular staple fibers, the cocarded mixturebeing in the form of an intimate, interentangled blend of saidmicrocellular and dense fibers.

2. The material of claim 1 wherein said polymer is crystalline and saidmicrocellular fibers are untramicrocellular fibers exhibiting uniplanarorientation and uniform texture.

3. The material of claim 2 wherein said ultramicrocellular fibers arecomposed of polyethylene terephthalate.

4. The material of claim 3 wherein said dense fibers are composed ofpolyethylene terephthalate.

5. The material of claim 1 wherein the cells of the microcellular fibersare fully inflated and contain an impermeant inflatant.

6. The material of claim 1 containing 25 to 65 percent by weight of saidmicrocellular fibers and 75 to 35 percent by weight of said densefibers, said microcellular fibers being composed of polyhedral-shapedcells having an average transverse dimension of less than 1,000 micronsand which contain an impermeant inflatant, said microcellular fibershaving a density of less than about 0.05 g./cc. and a diameter of lessthan about 0.4 inch.

7. A cushioning article containing the material of claim 1 as astuffing.

2. The material of claim 1 wherein said polymer is crystalline and saidmicrocellular fibers are untramicrocellular fibers exhibiting uniplanArorientation and uniform texture.
 3. The material of claim 2 wherein saidultramicrocellular fibers are composed of polyethylene terephthalate. 4.The material of claim 3 wherein said dense fibers are composed ofpolyethylene terephthalate.
 5. The material of claim 1 wherein the cellsof the microcellular fibers are fully inflated and contain an impermeantinflatant.
 6. The material of claim 1 containing 25 to 65 percent byweight of said microcellular fibers and 75 to 35 percent by weight ofsaid dense fibers, said microcellular fibers being composed ofpolyhedral-shaped cells having an average transverse dimension of lessthan 1,000 microns and which contain an impermeant inflatant, saidmicrocellular fibers having a density of less than about 0.05 g./cc. anda diameter of less than about 0.4 inch.
 7. A cushioning articlecontaining the material of claim 1 as a stuffing.